Add Bouncy Castle dependency.

See https://emu.freenetproject.org/pipermail/devl/2012-October/036588.html
for information on the minimum version.
Add Bouncy Castle to used libraries.
Update to split contrib and to Fred 1444.
Update changelog.
Update build instructions.
Merge pull request #3 from Thynix/update-1444-2

Update to Fred 1444; modular freenet-ext